1. Field of the Invention
The present invention relates to a method for manufacturing a magnetic recording medium in which a recording layer is formed into predetermined concavo-convex pattern over a substrate, and recessed portions of the concavo-convex pattern are filled with a non-magnetic material.
2. Description of the Related Art
In a conventional magnetic recording medium such as a hard disc, the areal density thereof has been increased remarkably by various technical improvements such as, making magnetic particles composing a recording layer finer, change materials to more effective ones, sophisticating of a head processing,and further improvement of the areal density is expected in the future.
However, problems such as the limitations of sophisticating of a head processing, a side fringe and crosstalk caused by the extent of a magnetic field have become conspicuous, so that the improvement of the areal density by use of conventional improving methods is approaching its limits. Accordingly, a discrete type magnetic recording medium is proposed as a candidate for a magnetic recording medium which can realize further improvement of the areal density (refer to, for example, Japanese Patent Laid-Open Publication No. Hei 9-97419). In this magnetic recording medium, a recording layer is formed into predetermined concavo-convex pattern and recessed portions of the concavo-convex pattern are filled with a non-magnetic material.
As the processing technique of forming the recording layer into the predetermined concavo-convex pattern, a method of dry etching such as reactive ion etching is available (refer to, for example, Japanese Patent Laid-Open Publication No. Hei 12-322710).
Processing techniques such as sputtering, which are used in a field of manufacturing a semiconductor, are available as methods for filling the non-magnetic material. When the processing techniques such as the sputtering are used, the surface of the non-magnetic material is formed into a concavo-convex shape by copying the concavo-convex pattern of the recording layer. The non-magnetic material is deposited on the top face of the recording layer, in addition to the recessed portions of the concavo-convex pattern.
To obtain the stable flying of the head, it is preferable to flatten the surfaces of the recording layer and the non-magnetic material. It is also preferable that any surplus non-magnetic material on the recording layer should be removed as much as possible in order to obtain a fine magnetic property. Processing techniques such as CMP (chemical mechanical polishing), which are used in the field of manufacturing a semiconductor, are available for removing the surplus non-magnetic material on the recording layer to flatten the surfaces of the recording layer and the non-magnetic material.
When the film thickness of the non-magnetic material is thin, however, the non-magnetic material is not completely filled into the recessed portion of the concavo-convex pattern, so that there are cases that the surfaces of the recording layer and the non-magnetic material cannot be adequately flattened.
Even if the non-magnetic material is completely filled into the recessed portions between the recording layers, when the film thickness of the non-magnetic material is thin, the surfaces of the recording layer and the non-magnetic material may not be adequately flattened. To be more specific, as shown in FIG. 21A, the surface of a non-magnetic material 102 is formed into a slightly concavo-convex shape by copying an concavo-convex shape of a recording layer 104. The non-magnetic material 102 is flattened with overall removal in an flattening process, and concavo-convex shape in the surface is gradually eliminated. If the film thickness of the non-magnetic material is thin, the flattening process having the effect of eliminating the concavo-convex shape in the surface becomes substantially short. Therefore, as shown in FIG. 21B, even if the non-magnetic material 102 is removed up to the top faces of the recording elements 104, the concavo-convex shape in the surface of the non-magnetic material 102 may not be adequately eliminated.
By contrast, depositing the non-magnetic material thicker can solve the foregoing problem, but brings another problem that efficiency in the use of material decreases and manufacturing cost increases. Also, there is a problem that time for the flattening process becomes long, and hence manufacturing efficiency decreases. Furthermore, the film thickness of the deposited non-magnetic material tends to vary in a constant proportion in accordance with areas on the substrate. Thus, when the non-magnetic material is thickly deposited, the distribution of film thickness (variations in film thickness) of the non-magnetic material becomes extensive. This may reduce the effect on flattening the surface by depositing the non-magnetic material thicker. Otherwise, the surface cannot be adequately flattened in the flattening process, and the degree of the concavo-convex shape in the surface of the magnetic recording medium may contrarily become larger.